Proper Router Routing, Two IP addresses?

I dont know whether we might be needing 2 ip addresses because we are moving to a new office. We have got SBS 2003 behind a Sonicwall TZ 170 Router. This was setup by someone else. So, we have for 2 ip addresses, one is for the router and the other for the mail server. I am sure that it was setup this was for a good reason. The issue that I am seeing is how the router is setup. The routers wan port goes directly to the DSL modem, also its "OPT. ZONE" port goes into the NIC card on our server. Its nomal and numbered port goes into our hub. The server's integrated NIC goes into the hub and its NIC card goes to the router as well. Why is it setup like this way? The router is supposed to be in between the outside world and the network, isnt it, but its plugged directly into the hub and the server is connected into both the router and the hub? Thanks for any information

Incase you want to run 2 version of the same service on different machines then you will need 2 ip addresses. If you wanted to make the SBS web services available to its domain users from outside the network on HTTP, port 80 and you also wanted to run a public server, then the only safe way is to use 2 separate machines, isolated from each other, and you may have no options but to use 2 different ip addresses.

As per your discussion, I think you want to know how to setup your SBS network and IP address. You can try to configure SBS to not be a DHCP server, first use the following steps to stop and disable the DHCP Server service, given on this website - http://support.microsoft.com/kb/303301